The invention is generally directed to truss joists constructed from metal webs and lumber chords well known as a structural member for use in bridges and buildings for over 100 years.
Two basic types of truss joists are the single chord and double chord truss. A standard double chord truss joist has two spaced chord sections with each chord section comprising two juxtaposed lumber sections placed side by side parallel to each other. Each lumber section has registered openings. Metal webs diagonally span these chord sections usually in zig-zag fashion with adjacent web ends being overlapped. Each end of the webs is flattened and has a central aperture registered between the juxtaposed lumber section openings of each chord. Metal pins extend through these apertures into the lumber section openings thereby fastening the webs to the wooden chords.
A standard single chord truss joist assembly has two spaced chord sections each having an opposing face which is slotted. Each of the chord sections also has a transverse opening drilled through the section in communication with the slot. Metal webs, of the same type as discussed above, diagonally span the chord sections in overlapping zig-zag fashion. The flattened apertured web ends extend into the chord slots and are secured to the chords by a pin which passes through the transverse chord section opening and the apertured web end.
The pins are typically retained within the single and double trusses by means of an external assembly, such as a locking washer, which fits over each end of the pin protruding from the wooden chords. Such external assemblies, although satisfactory, may interfere with use of the trusses in construction or may become dislodged. There is, therefore, a need for a pin/chord assembly which will provide for automatic and effective locking of the pin within the chord opening upon insertion.
Secondly, unbalanced or impact loads on the truss have produced vibrational problems in the past. Moreover, the truss is not constructed to provide dampening of undesirable noise created by the working of the truss. Thus, a mechanism that would absorb vibrations and sound would be quite advantageous.
Finally, although the pin and the steel web members are capable of sustaining very high stresses, problems have resulted in the past because the wood chord has a tendency to split at the joint. In fact, occasionally the metal pin will damage the wooden chord simply upon insertion. Although the low stress value, due to wood chord splitting, has been a well-identified problem for several years, the truss industry has yet to devise a satisfactory solution.
U.S. Pat. Nos. 3,985,459 and 3,946,532 disclose perforated plates having a plurality of tooth-like projections which mount the plates to the truss chords. A central aperture is formed in each of the plates having an annular rim to yield an increased bearing surface for the plates. In this regard, the '532 patent further discloses the use of a hollow sleeve which extends through the web members and into the central aperture of the plate to transfer the load exerted on the web members directly to the plates.
U.S. Pat. Nos. 3,330,087 and 3,336,706 disclose the use of a hollow cylindrical pin of high strength material which fits snugly within the registered openings of the chord and web. These pins are particularly adapted to be used in conjunction with bearing clips at the terminal ends of the truss. In this construction, the vertical load of the truss is transferred through the web and hollow pin, to the support provided by the bearing clips.
One disadvantage of the above structures is that the diameter of the aperture through the web members must be approximately the same size as the opening in the chord. Thus, the obtainable bearing area in the wood chords is limited by the size of the web apertures. Another disadvantage is that external washers are required to lock the pins in place. Finally, the metal pins may cause the wood to splinter upon insertion, do not conform to irregularities in the chord openings, and provide no vibrational or sound absorption.
Thus, although trusses have existed for over a century, there still remains a need for an improved means to effect the web/chord joint.